The disclosure of the present disclosure relates to a light-emitting device.
Examples of light-emitting devices that employ light-emitting diodes (hereinafter also referred to as “LEDs”) to emit white light include a light-emitting device employing a combination of a LED capable of emitting blue light and a phosphor capable of emitting yellow light. This light-emitting device emits white light as a mixture of the colors of blue light emitted from the LED and yellow light emitted from the phosphor excited by the blue light. Such a light-emitting device shows high emission intensity and efficiency in the visible region but does not provide sufficient emission intensity in the blue-green and red regions in some cases. Hence, how the color of an irradiated object looks (hereinafter referred to as “color rendering properties”) has room for further improvement.
The method of specifying color rendering properties of light sources defined by JIS Z 8726 includes numerically calculating the color difference ΔEi (where i is an integer from 1 to 15) between measurements of a test color (R1 to R15), which has predetermined reflectance properties, under a test light source and the reference light source to calculate a color rendering index. The upper limit of the color rendering index Ri (where i is an integer from 1 to 15) is 100. In other words, the smaller the color difference between the test light source and the reference light source having the color temperature corresponding to the test light source is, the higher and closer to 100 the color rendering index is. Among color rendering indices, the average value of R1 to R8 is called the general color rendering index (hereinafter also referred to as Ra), and special color rendering indices are obtained by using R9 to R15. For the special color rendering indices, R9 is defined as red, R10 as yellow, R11 as green, R12 as blue, R13 as the skin color of Westerners, R14 as the color of tree leaves, and R15 as the skin color of Japanese.
For example, WO2001/093341 discloses a light-emitting device including an light emitting element and two types of phosphors that emit green to yellow light, such as a chlorosilicate phosphor and a garnet phosphor containing Y or Tb, in order to improve the color rendering properties of the light source. Also, Japanese Unexamined Patent Application Publication No. 2008-034188 proposes a light-emitting device including a phosphor that emits red light in addition to a phosphor that emits green to yellow light in order to further improve the color rendering properties.
In addition, Japanese Unexamined Patent Application Publication No. 2010-207278 proposes a surface sterilization method that achieves sterilization without exerting harmful effects on the human body by radiating light (near-ultraviolet light) with a maximum intensity at 400 nm to 410 nm.
The present disclosure has an object to provide a light-emitting device that has good color rendering properties and can alleviate the proliferation of germs.